Laser methods for processing electrochromic glass

ABSTRACT

Techniques for laser processing of a workpiece including electrochromic glass or other thin-film devices where one or more layers are sandwiched between two thin-film conductive layers include directing a laser beam from a laser source onto a surface of the workpiece, wherein the laser beam comprises projected light, the projected light having a selected near-infrared wavelength in the range of about 1.4 to about 3 μm. Where the workpiece comprises an electrochromic device including an electrochromic stack disposed between a first transparent conductive layer, distal from the laser source, and a second transparent conductive layer, proximal to the laser source, removing the material includes removing a portion of the second transparent conductive layer and a portion of the electrochromic stack to expose a surface of the first transparent conductive layer without damaging the first transparent conductive layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

An Application Data Sheet is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed Application Data Sheet is incorporated by reference herein in its entirety and for all purposes.

TECHNICAL FIELD

Embodiments disclosed herein relate generally to optical devices, and more particularly to methods of fabricating optical devices.

BACKGROUND

Electrochromism is a phenomenon in which a material exhibits a reversible electrochemically-mediated change in an optical property when placed in a different electronic state, typically by being subjected to a voltage change. The optical property is typically one or more of color, transmittance, absorbance, and reflectance. For example, one well known electrochromic material is tungsten oxide (WO₃). Tungsten oxide is a cathodically coloring electrochromic material in which a coloration transition, bleached (non-colored) to blue, occurs by electrochemical reduction. When electrochemical oxidation takes place, tungsten oxide transitions from blue to a bleached state.

Electrochromic materials may be incorporated into, for example, windows for home, commercial and other uses. The color, transmittance, absorbance, and/or reflectance of such windows may be changed by inducing a change in the electrochromic material, that is, electrochromic windows are windows that can be darkened and lightened reversibly via application of an electric charge. A small voltage applied to an electrochromic device of the window will cause it to darken; reversing the voltage causes it to lighten. This capability allows control of the amount of light that passes through the windows and presents an opportunity for electrochromic windows to be used as energy-saving devices.

Improved fabrication techniques of electrochromic devices for electrochromic devices, and/or other thin-film devices where one or more layers are sandwiched between two thin-film conductive layers are desirable. In addition to electrochromic devices, flat panel displays, photovoltaic devices, suspended particle devices (SPD's), liquid crystal devices (LCD's) may benefit from the techniques described hereinbelow.

SUMMARY

Certain embodiments of this disclosure pertain to methods of removing a material from a surface of a workpiece. The workpiece may be any structure having a material that can be fully or partially removed or otherwise modified by one or more lasers. In some embodiments, the workpiece is a window or other structure comprising an optically switchable device. In certain embodiments, the workpiece is an electrochromic device or a partially fabricated electrochromic device on a transparent substrate. The electrochromic device comprises one or more layers such as an electrochromic stack between two transparent conductive layers. The transparent conductive layers are electrically isolated from one another and independently addressable. They may be electrically controllable by bus bars or other attached electrically conductive structure.

In accordance with some embodiments, a method of removing the material may be characterized by directing a laser beam from a laser source onto a surface of the workpiece, wherein the laser beam comprises projected light, the projected light having a selected near-infrared wavelength in the range of about 1.4 to about 3 μm. The material may be removed by laser ablation.

In certain embodiments, the workpiece comprises an electrochromic device or a partially fabricated electrochromic device on a transparent substrate, and the material comprises one or more layers of the electrochromic device. In some examples, removing the material produces an ablation region on the one or more layers of the electrochromic device, the ablation region having at least one edge. In some examples, the edge may be approximately orthogonal to the one or more layers. In some examples, the edge may have a stepped or tapered profile.

In certain embodiments, removing the material forms a bus bar pad expose region. In some examples, the workpiece may include an electrochromic device including an electrochromic stack disposed between a first transparent conductive layer, distal from the laser source, and a second transparent conductive layer, proximal to the laser source, and removing the material may include comprises removing a portion of the second transparent conductive layer and a portion of the electrochromic stack to expose a surface of the first transparent conductive layer without damaging the first transparent conductive layer. In some examples, the bus bar pad expose region may include an exposed portion of the surface of the first transparent conductive layer.

In some implementations, the selected wavelength may be within a range of 1.8 μm to 2.2 μm.

In some implementations, the laser beam may remove the material from the workpiece by ablation.

In some implementations, removing the material may not comprise moving the laser beam in a raster scan.

In some implementations, wherein the laser source may include a thulium laser operating at a selected wavelength of about 1.95 μm or a holmium laser operating at a selected wavelength of about 2.05 μm.

In some implementations, the laser source may be configured to deliver a pulsed laser beam, each pulse having an energy in a range of about 200 to 1500 mJ. In some examples, the float glass substrate has a surface area greater than 40 square feet.

In accordance with some embodiments, a material removal system includes a laser source configured to direct a laser beam onto a surface of a workpiece, wherein the laser beam comprises projected light, the projected light having a selected near-infrared wavelength the range of about 1.4 to about 3 μm, and a workpiece holder. The laser and the workpiece holder are configured such that, during operation, the laser beam ablates material from the workpiece.

In some implementations, the workpiece may include an electrochromic device or a partially fabricated electrochromic device on a transparent substrate, and the material comprises one or more layers of the electrochromic device. In some examples, removing the material may produce an ablation region on the one or more layers of the electrochromic device, the ablation region having at least one edge. In some examples, the edge may be approximately orthogonal to the one or more layers. In some examples, the edge may have a stepped or tapered profile.

In some implementations, removing the material may form a bus bar pad expose region. In some examples, the workpiece may include an electrochromic device including an electrochromic stack disposed between a first transparent conductive layer, distal from the laser source, and a second transparent conductive layer, proximal to the laser source, and removing the material may include removing a portion of the second transparent conductive layer and a portion of the electrochromic stack to expose a surface of the first transparent conductive layer without damaging the first transparent conductive layer. In some examples, the bus bar pad expose region comprises an exposed portion of the surface of the first transparent conductive layer.

In some implementations, the laser source may include a thulium laser operating at a selected wavelength of about 1.95 μm or a holmium laser operating at a selected wavelength of about 2.05 μm.

In some implementations, the laser source may be configured to deliver a pulsed laser beam, each pulse having an energy in a range of about 200 to 1500 mJ. In some examples, each pulse may have a duration of from about 1 ns to about 100 ns. In some examples, the pulsed laser beam has a pulse repetition rate of about 1 to 100,000 Hz.

In some implementations, the workpiece may include a large-area float glass substrate.

In accordance with some embodiments, a structure includes a substrate and an electrochromic device disposed on the substrate, the electrochromic device including an electrochromic stack disposed between a first transparent conductive layer, distal from a laser source, a second transparent conductive layer, proximal to the laser source, and an ablation region. The ablation is produced by removing a portion of the second transparent conductive layer and a portion of the electrochromic stack without damaging the first transparent conductive layer.

In some implementations, the ablation region may have at least one edge. In some examples, the edge may be approximately orthogonal to the one or more layers. In some examples, the edge may have a stepped or tapered profile.

In some implementations, the ablation region may include a bus bar pad expose region. In some examples, the bus bar pad expose region may include an exposed portion of the surface of the first transparent conductive layer.

In some implementations, the structure may further include a large-area float glass substrate. In some examples, the float glass substrate may have a surface area greater than 40 square feet.

In accordance with some embodiments, a method of fabricating an optical device includes removing material from the optical device by directing a laser beam from a laser source onto a surface of the optical device, the optical device comprising a substrate and an electrochromic stack, the electrochromic stack being disposed between a first transparent conductive layer, distal from the laser source, and a second transparent conducting layer, proximal to the laser source. Removing the material includes removing a portion of the second transparent conductive layer and a portion of the electrochromic stack without damaging the first transparent conductive layer. The laser beam includes projected light, the projected light having a selected near-infrared wavelength in the range of about 1.4 to about 3 μm.

In some implementations, removing the material may produce an ablation region on the electrochromic stack, the ablation region having at least one edge. In some examples, the edge may be approximately orthogonal to the one or more layers. In some examples, the edge may have a stepped or tapered profile.

In some implementations, removing the material may form a bus bar pad expose region. In some examples, the bus bar pad expose region may include an exposed portion of the surface of the first transparent conductive layer.

In some implementations, the laser source may include a thulium laser operating at a selected wavelength of about 1.95 μm or a holmium laser operating at a selected wavelength of about 2.05 μm.

In some implementations, the laser source may be configured to deliver a pulsed laser beam, each pulse having an energy in a range of about 200 to 1500 mJ. In some examples, each pulse may have a duration of from about 1 ns to about 100 ns. In some example, the pulsed laser beam may have a pulse repetition rate of about 1 to 100,000 Hz.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description can be more fully understood when considered in conjunction with the drawings in which:

FIGS. 1A, 1B, and 1C are cross-section, end view, and top view drawings respectively of an electrochromic device fabricated on a glass substrate.

FIG. 2 is a partial cross-section of an electrochromic device architecture on a substrate.

FIG. 3 is a partial cross-section showing device architecture where the diffusion barrier is removed along with the lower conducting layer.

FIG. 4A is a flowchart of a process flow describing aspects of a method of fabricating an electrochromic device.

FIG. 4B are top views depicting steps in the process flow described in relation to FIG. 4A.

FIG. 4C depicts cross-sections of the electrochromic lite described in relation to FIG. 4B.

FIG. 4D is a schematic drawing of top views of devices similar to that described in relation to FIG. 4B.

FIG. 4E is a schematic drawing in the perspective view depicting fabrication of an IGU with an optical device.

FIGS. 4F and 4G are schematic drawings depicting steps of a process flow similar to that described in relation to FIG. 4A and carried out on a large-area substrate as applied to coat then cut methods.

FIG. 5 illustrates a comparison of laser ablation according to the prior art with the presently disclosed techniques.

FIG. 6 illustrates a method for fabricating an optical device according to some embodiments.

FIG. 7 illustrates features of a selective ablation process, according to some embodiments.

FIG. 8 illustrates a comparison between a depth profile of an ablation region produced by conventional ablation techniques with one produced by a selective ablation process, according to some embodiments.

FIG. 9A illustrates a cross-section view of a scribe line formed using a selective ablation process, according to some embodiments.

FIG. 9B illustrates a cross-section view of a scribe line formed using conventional ablation process.

FIG. 10 illustrates two examples of how tapered or stepped sidewalls may be obtained, according to some embodiments.

FIG. 11 illustrates a method for fabricating an optical, according to some embodiments.

DETAILED DESCRIPTION

Details of one or more implementations of the subject matter described in this specification are set forth in this disclosure, which includes the description and claims in this document and the accompanying drawings.

Certain embodiments are directed to optical devices, that is, thin-film devices having at least one transparent conductor layer. In the simplest form, an optical device includes a substrate and one or more material layers sandwiched between two conductor layers, one of which is transparent. In one embodiment, an optical device includes a transparent substrate and two transparent conductor layers. In another embodiment, an optical device includes a transparent substrate upon which is deposited a transparent conductor layer (the lower conductor layer) and the other (upper) conductor layer is not transparent. In another embodiment, the substrate is not transparent, and one or both of the conductor layers is transparent. Some examples of optical devices include electrochromic devices, flat panel displays, photovoltaic devices, suspended particle devices (SPD's), liquid crystal devices (LCD's), and the like. For context, a description of electrochromic devices is presented below. For convenience, all solid-state and inorganic electrochromic devices are described; however, embodiments are not limited in this way. Particular focus is given to methods of patterning and fabricating optical devices. Various edge deletion and isolation scribes are performed, for example, to ensure the optical device has appropriate isolation from any edge defects, but also to address unwanted coloration and charge buildup in areas of the device. Edge treatments are applied to one or more layers of optical devices during fabrication. Methods described herein apply to any thin-film device having one or more material layers sandwiched between two thin-film electrical conductor layers.

For the purposes of brevity, embodiments are described in terms of electrochromic devices; however, the scope of the disclosure is not so limited. One of ordinary skill in the art would appreciate that methods described can be used to fabricate virtually any thin-film device where one or more layers are sandwiched between two thin-film conductor layers. Certain embodiments are directed to optical devices, that is, thin-film devices having at least one transparent conductor layer. In the simplest form, an optical device includes a substrate and one or more material layers sandwiched between two conductor layers, one of which is transparent. In one embodiment, an optical device includes a transparent substrate and two transparent conductor layers. In another embodiment, an optical device includes a transparent substrate upon which is deposited a transparent conductor layer (the lower conductor layer) and the other (upper) conductor layer is not transparent. In another embodiment, the substrate is not transparent, and one or both of the conductor layers is transparent. Some examples of optical devices include electrochromic devices, flat panel displays, photovoltaic devices, suspended particle devices (SPD's), liquid crystal devices (LCD's), and the like. For context, a description of electrochromic devices is presented below. For convenience, all solid-state and inorganic electrochromic devices are described, such as those contemplated by U.S. patent application Ser. No. 15/109,624, filed Oct. 12, 2016, entitled “Thin Film Devices and Fabrication”, assigned to the assignee of the present invention, and hereby incorporated by reference in its entirety; however, embodiments are not limited in this way.

A particular example of an electrochromic (EC) lite is described with reference to FIGS. 1A-1C, in order to illustrate embodiments described herein. The electrochromic lite includes an electrochromic device fabricated on a substrate. FIG. 1A is a cross-sectional representation (see cut X-X′ of FIG. 1C) of an electrochromic lite, 100, which is fabricated starting with a glass sheet, 105. FIG. 1B shows an end view (see perspective Y-Y′ of FIG. 1C) of electrochromic lite 100, and FIG. 1C shows a top-down view of electrochromic lite 100.

FIG. 1A shows the electrochromic lite 100 after fabrication on glass sheet 105 and the edge has been deleted to produce area 140 around the perimeter of the lite. Edge deletion refers to removing one or more material layers from the device about some perimeter portion of the substrate. Typically, though not necessarily, edge deletion removes material down to and including the lower conductor layer (e.g., layer 115 in the example depicted in FIGS. 1A-1C), and may include removal of any diffusion barrier layer(s) down to the substrate itself. In FIGS. 1A-1B, the electrochromic lite 100 has also been laser scribed and bus bars have been attached. The glass lite, 105, has a diffusion barrier, 110, and a first transparent conducting oxide (TCO) layer 115 disposed on the diffusion barrier 110.

In this example, a laser edge deletion (“LED”) process removes both the first TCO layer 115 and the diffusion barrier 110, but in other embodiments, only the first TCO layer 115 is removed, leaving the diffusion barrier intact. The TCO layer 115 is the first of two conductive layers used to form the electrodes of the electrochromic device fabricated on the glass sheet. In some examples, the glass sheet may be prefabricated with the diffusion barrier formed over underlying glass. Thus, the diffusion barrier is formed, and then the first TCO 115, an EC stack 125 (e.g., stack having electrochromic, ion conductor, and counter electrode layers), and a second TCO, 130, are formed. In other examples, the glass sheet may be prefabricated with both the diffusion barrier and the first TCO 115 formed over underlying glass.

In certain embodiments, one or more layers may be formed on a substrate (e.g., glass sheet) in an integrated deposition system where the substrate does not leave the integrated deposition system at any time during fabrication of the layer(s). In one embodiment, an electrochromic device including an EC stack and a second TCO may be fabricated in the integrated deposition system where the glass sheet does not leave the integrated deposition system at any time during fabrication of the layers. In one case, the first TCO layer may also be formed using the integrated deposition system where the glass sheet does not leave the integrated deposition system during deposition of the EC stack, and the TCO layer(s). In one embodiment, all of the layers (e.g., diffusion barrier, first TCO, EC stack, and second TCO) are deposited in the integrated deposition system where the glass sheet does not leave the integrated deposition system during deposition. In this example, prior to deposition of EC stack 125, an isolation trench, 120, may be cut through first TCO 115 and diffusion barrier 110. Trench 120 is made in contemplation of electrically isolating an area of first TCO 115 that will reside under bus bar 1 after fabrication is complete (see FIG. 1A). Trench 120 is sometimes referred to as the “L1” scribe, because it is the first laser scribe in certain processes. This may be done to avoid charge buildup and coloration of the EC device under the bus bar, which can be undesirable.

After formation of the EC device, LED processes and additional laser scribing may be performed. FIGS. 1A and 1B depict areas 140 where the EC device has been removed, in this example, from a perimeter region surrounding laser scribe trenches, 150, 155, 160 and 165. Laser scribes 150, 160 and 165 are sometimes referred to as “L2” scribes, because they are the second scribes in certain processes. Laser scribe 155 is sometimes referred to as the “L3” scribe, because it is the third scribe in certain processes. The L3 scribe passes through second TCO, 130, and in this example (but not necessarily) the EC stack 125, but not the first TCO 115. Laser scribe trenches 150, 155, 160, and 165 are made to isolate portions of the EC device, 135, 145, 170, and 175, which were potentially damaged during edge deletion processes from the operable EC device.

The laser or lasers used for the laser scribe processes are typically, but not necessarily, pulse-type lasers, for example, diode-pumped solid state lasers. For example, the laser scribe processes can be performed using a suitable laser. Some examples of suppliers that may provide suitable lasers include IPG Photonics Corp. (of Oxford, Mass.), Ekspla (of Vilnius, Lithuania), TRUMPF Inc. (Farmington, Conn.), SPI Lasers LLC (Santa Clara, Calif.), Spectra-Physics Corp. (Santa Clara, Calif.), nLIGHT Inc. (Vancouver, Wash.), and Fianium Inc. (Eugene, Oreg.). Certain scribing steps can also be performed mechanically, for example, by a diamond tipped scribe; however, certain embodiments describe depth control during scribes or other material removal processing, which is well controlled with lasers. For example, in one embodiment, edge deletion is performed to the depth of the first TCO, in another embodiment edge deletion is performed to the depth of a diffusion barrier (the first TCO is removed), in yet another embodiment edge deletion is performed to the depth of the substrate (all material layers removed down to the substrate). In certain embodiments, variable depth scribes are described.

After laser scribing is complete, bus bars are attached. Non-penetrating bus bar (1) is applied to the second TCO. Non-penetrating bus bar (2) is applied to an area where the device including an EC stack and a second TCO was not deposited (for example, from a mask protecting the first TCO from device deposition) or, in this example, where an edge deletion process (e.g. laser ablation using an apparatus e.g. having a XY or XYZ galvanometer) was used to remove material down to the first TCO. In this example, both bus bar 1 and bus bar 2 are non-penetrating bus bars. A penetrating bus bar is one that is typically pressed into (or soldered) and through one or more layers to make contact with a lower conductor, e.g. TCO located at the bottom of or below one or more layers of the EC stack). A non-penetrating bus bar is one that does not penetrate into the layers, but rather makes electrical and physical contact on the surface of a conductive layer, for example, a TCO. A typical example of a non-penetrating bus bar is a conductive ink, e.g. a silver-based ink, applied to the appropriate conductive surface.

The TCO layers can be electrically connected using a non-traditional bus bar, for example, a bus bar fabricated with screen and lithography patterning methods. For example, electrical communication may be established with the device's transparent conducting layers via silk screening (or using another patterning method) a conductive ink followed by heat curing or sintering the ink. Advantages to using the above described device configuration include simpler manufacturing, for example, and less laser scribing than conventional techniques which use penetrating bus bars.

After the bus bars are fabricated or otherwise applied to one or more conductive layers, the electrochromic lite may be integrated into an insulated glass unit (IGU), which includes, for example, wiring for the bus bars and the like. In some embodiments, one or both of the bus bars are inside the finished IGU. In particular embodiments, both bus bars are configured between the spacer and the glass of the IGU (commonly referred to as the primary seal of the IGU); that is, the bus bars are registered with the spacer used to separate the lites of an IGU. Area 140 is used, at least in part, to make the seal with one face of the spacer used to form the IGU. Thus, the wires or other connection to the bus bars runs between the spacer and the glass. As many spacers are made of metal, e.g., stainless steel, which is conductive, it is desirable to take steps to avoid short circuiting due to electrical communication between the bus bar and connector thereto and the metal spacer. Particular methods and apparatus for achieving this end are described in U.S. patent application Ser. No. 13/312,057, filed Dec. 6, 2011, and titled “Improved Spacers for Insulated Glass Units,” which is hereby incorporated by reference in its entirety. In certain embodiments described herein, methods and resulting IGUs include having each of the perimeter edge of the EC device, bus bars and any isolation scribes within the primary seal of the IGU.

FIG. 2 is a partial cross-section showing an EC device 200 of a second configuration. In the illustrated example, the portion of first TCO 115 that would have extended below bus bar 1 is removed prior to fabrication of EC stack 125. In this example, diffusion barrier 110 extends to under bus bar 1 and to the edge of the EC device. In some examples, the diffusion barrier extends to the edge of glass 105, that is, it covers area 140. In other examples, a portion of the diffusion barrier may also be removed under the bus bar 1. In the aforementioned examples, the selective TCO removal under bus bar 1 is performed prior to fabrication of EC stack 125. Edge deletion processes to form areas 140 (e.g., around the perimeter of the glass where the spacer forms a seal with the glass) can be performed prior to device fabrication or after. An isolation scribe trench, 150 a, may be formed if the edge delete process to form 140 creates a rough edge or otherwise unacceptable edge due to, e.g., shorting issues, thus isolating a portion, 135 a, of material from the remainder of the EC device. As exemplified in the expanded portion of EC device 200 depicted in FIG. 2, since there is no portion of TCO 115 under bus bar 1, the aforementioned problems such as unwanted coloring and charge buildup may be avoided. Also, since diffusion barrier 110 is left intact, at least co-extensive with EC stack 125, sodium ions are prevented from diffusing into the EC stack 125 and causing unwanted conduction or other problems.

FIG. 3 is a partial cross-section showing electrochromic device architecture, 300 of yet a further configuration. In the illustrated example, the portions of TCO 115 and diffusion barrier 110 that would have extended below bus bar 1 are removed prior to fabrication of EC stack 125. That is, the first TCO and diffusion barrier removal under bus bar 1 is performed prior to fabrication of EC stack 125. LED processes to form areas 140 (e.g., around the perimeter of the glass where the spacer forms a seal with the glass) can be performed prior to device fabrication (e.g., removing the diffusion barrier and using a mask thereafter) or after device fabrication (removing all materials down to the glass). An isolation scribe trench, analogous to 150 a in FIG. 2, may be formed if the edge deletion process to form 140 creates a rough edge, thus isolating a portion, 135 a (see FIG. 2), of material from the remainder of the EC device.

Techniques for fabricating an optical device including one or more material layers sandwiched between a first conducting layer (e.g., first TCO 115) and a second conducting layer (e.g., second TCO 130) may include: (i) receiving a substrate including the first conducting layer over its work surface; (ii) removing a first width of the first conducting layer from between about 10% and about 90% of the perimeter of the substrate; (iii) depositing the one or more material layers of the optical device and the second conducting layer such that they cover the first conducting layer and, where possible, extend beyond the first conducting layer about its perimeter; (iv) removing a second width, narrower than the first width, of all the layers about substantially the entire perimeter of the substrate, where the depth of removal is at least sufficient to remove the first conducting layer; (v) removing at least one portion of the second transparent conducting layer and the one or more layers of the optical device thereunder thereby revealing at least one exposed portion of the first conducting layer; and (vi) applying a bus bar to the at least one exposed portion of the first transparent conducting layer; where at least one of the first and second conducting layers is transparent.

FIG. 4A is a process flow, 400, describing aspects of a method of fabricating an electrochromic device or other optical device having opposing bus bars, each applied to one of the conductor layers of the optical device. The dotted lines denote optional steps in the process flow. An exemplary device, 440, as described in relation to FIGS. 4B-C, is used to illustrate the process flow. FIG. 4B provides top views depicting the fabrication of device 440 including numerical indicators of process flow 400 as described in relation to FIG. 4A. FIG. 4C shows cross-sections of the lite including device 440 described in relation to FIG. 4B. Device 440 is a rectangular device, but process flow 400 applies to any shape of optical device having opposing bus bars, each on one of the conductor layers.

Referring to FIGS. 4A and 4B, after receiving a substrate with a first conductor layer thereon, process flow 400 begins with an optional polishing of the first conductor layer, see 401. Polishing a lower transparent conductor layer may enhance the optical properties of, and performance of, EC devices fabricated thereon. Polishing of transparent conducting layers prior to electrochromic device fabrication thereon is described in patent application, PCT/US12/57606, titled, “Optical Device Fabrication,” filed on Sep. 27, 2012, which is hereby incorporated by reference in its entirety. Polishing, if performed, may be done prior to an LED process, see 405, or after an LED in the process flow. In some examples, the lower conductor layer may be polished both before and after edge deletion. Typically, the lower conductor layer is polished only once.

Referring again to FIG. 4A, if polishing 401 is not performed, process 400 begins with edge deleting a first width about a portion of the perimeter of the substrate, see 405. The edge deletion may remove only the first conductor layer or may also remove a diffusion barrier, if present. In one embodiment, the substrate is glass and includes a sodium diffusion barrier and a transparent conducting layer thereon, e.g. a tin-oxide based transparent metal oxide conducting layer. The substrate may be rectangular (e.g., the square substrate depicted in see FIG. 4B). The dotted area in FIG. 4B denotes the first conductor layer. Thus, after edge deletion according to process 405, a width A is removed from three sides of the perimeter of substrate 430. This width is typically, but not necessarily, a uniform width. A second width, B, is described below. Where width A and/or width B are not uniform, then their relative magnitudes with respect to each other are in terms of their average width.

As a result of the removal of the first width A at 405, there is a newly exposed edge of the lower conductor layer. Optionally, at least a portion of this edge of the first conductive layer may be optionally tapered, see 407 and 409. The underlying diffusion barrier layer may also be tapered.

The lower conductor layer may also, optionally, be polished after edge tapering, see 408. It has been found, that with certain device materials, it may be advantageous to polish the lower conductor layer after the edge taper. For example, the edge taper may be performed after polish 408, see 409. Although edge tapering is shown at both 407 and 409 in FIG. 4A, if performed, edge tapering would typically be performed once (e.g., at 407 or 409).

After removal of the first width A, and optional polishing and/or optional edge tapering as described above, the EC device is deposited over the surface of substrate 430, see 410. This deposition includes one or more material layers of the optical device and the second conducting layer, e.g. a transparent conducting layer such as indium tin oxide (ITO).

The LED process may be performed at least to remove material including the transparent conductor layer on the substrate, and optionally also removing a diffusion barrier if present. In certain embodiments, edge deletion is used to remove a surface portion of the substrate, e.g. float glass, and may go to a depth not to exceed the thickness of the compression zone. Edge deletion is performed, e.g., to create a good surface for sealing by at least a portion of the primary seal and the secondary seal of the IGU. For example, a transparent conductor layer can sometimes lose adhesion when the conductor layer spans the entire area of the substrate and thus has an exposed edge, despite the presence of a secondary seal. Also, it is believed that when metal oxide and other functional layers have such exposed edges, they can serve as a pathway for moisture to enter the bulk device and thus compromise the primary and secondary seals.

LED is described herein as being performed on a substrate that is already cut to size. However, edge deletion can be done before a substrate is cut from a bulk glass sheet in other disclosed embodiments. For example, non-tempered float glass may be cut into individual lites after an EC device is patterned thereon. Methods described herein can be performed on a bulk sheet and then the sheet cut into individual EC lites. In certain embodiments, edge deletion may be carried out in some edge areas prior to cutting the EC lites, and again after they are cut from the bulk sheet. In certain embodiments, all edge deletion is performed prior to excising the lites from the bulk sheet. In embodiments employing “edge deletion” prior to cutting the panes, portions of the coating on the glass sheet can be removed in anticipation of where the cuts (and thus edges) of the newly formed EC lites will be. In other words, there is no actual substrate edge yet, only a defined area where a cut will be made to produce an edge. Thus “edge deletion” is meant to include removing one or more material layers in areas where a substrate edge is anticipated to exist. Methods of fabricating EC lites by cutting from a bulk sheet after fabrication of the EC device thereon are described in U.S. patent application Ser. No. 12/941,882 (now U.S. Pat. No. 8,164,818), filed Nov. 8, 2010, and U.S. patent application Ser. No. 13/456,056, filed Apr. 25, 2012, each titled “Electrochromic Window Fabrication Methods” each of which is hereby incorporated by reference in its entirety.

In some examples, material may be removed by laser ablation. The ablation can be performed from either the substrate side or the EC film side depending on the choice of the substrate handling equipment and configuration parameters.

Conventionally, the energy density required to ablate the film thickness has been achieved by passing the laser beam through an optical lens. The lens focuses the laser beam to the desired shape and size. For example, a “top hat” beam configuration has been used, e.g., having a focus area of between about 0.005 mm2 to about 2 mm2. The focusing level of the beam has been selected to achieve the required energy density to ablate the EC film stack. For example the energy density used in the ablation may be between about 2 J/cm2 and about 6 J/cm2.

During a laser edge delete process, a laser spot may be scanned over the surface of the EC device, along the periphery. Homogeneous removal of the EC film is desired, and this has been accomplished by, for example, overlapping the spots' area during scanning, the overlap extending, in known examples, between about 5% and about 100%, between about 10% and about 90%, and between about 10% and about 80%. Various scanning patterns have been used, e.g., scanning in straight lines, curved lines, and various patterns may be scanned, e.g., rectangular or other shaped sections are scanned which, collectively, create the peripheral edge deletion area. The scanning lines (or “pens,” i.e. lines created by adjacent or overlapping laser spots, e.g. square, round, etc.) may be overlapped at the levels described above for spot overlap. That is, the area of the ablated material defined by the path of the line previously scanned is overlapped with later scan lines so that there is overlap. That is, a pattern area ablated by overlapping or adjacent laser spots is overlapped with the area of a subsequent ablation pattern. Where overlapping is needed, spots, lines or patterns, a higher frequency laser, e.g. in the range of between about 11 KHz and about 500 KHz, may be used.

Referring again to FIGS. 4A and 4B, process flow 400 continues with removing a second width, B, narrower than the first width A, about substantially the entire perimeter of the substrate, see 415. This may include removing material down to the glass or to a diffusion barrier, if present. After process flow 400 is complete up to 415, e.g. on a rectangular substrate as depicted in FIG. 4B, there is a perimeter area, with at least width B, where there is none of the first transparent conductor, the one or more material layers of the device, or the second conducting layer—removing width B has exposed diffusion barrier or substrate. Within this perimeter area is the device stack, including the first transparent conductor surrounded on three sides by overlapping one or more material layers and the second conductor layer. On the remaining side (e.g., the bottom side in FIG. 4B) there is no overlapping portion of the one or more material layers and the second conductor layer. It is proximate this remaining side (e.g., bottom side in FIG. 4B) that the one or more material layers and the second conductor layer are removed in order to expose a portion (bus bar pad expose, or “BPE”), 435, of the first conductor layer, see 420. The BPE 435 need not run the entire length of that side, it need only be long enough to accommodate the bus bar and leave some space between the bus bar and the second conductor layer so as not to short on the second conductor layer. In one embodiment, the BPE 435 spans the length of the first conductor layer on that side.

As described above, a BPE is where a portion of the material layers are removed down to the lower electrode or other conductive layer (e.g. a transparent conducting oxide layer), in order to create a surface for a bus bar to be applied and thus make electrical contact with the electrode. The bus bar applied can be a soldered bus bar, and ink bus bar and the like. A BPE typically has a rectangular area, but this is not necessary; the BPE may be any geometrical shape or an irregular shape. For example, depending upon the need, a BPE may be circular, triangular, oval, trapezoidal, and other polygonal shapes. The shape may be dependent on the configuration of the EC device, the substrate bearing the EC device (e.g. an irregular shaped window), or even, e.g., a more efficient (e.g. in material removal, time, etc.) laser ablation pattern used to create it. Typically, but not necessarily, the BPE is wide enough to accommodate the bus bar, but should allow for some space at least between the active EC device stack and the bus bar. As mentioned, a bus bar may be between about 1 mm and about 5 mm wide, typically about 3 mm wide.

As mentioned, the BPE is, advantageously, fabricated wide enough to accommodate the bus bar's width and also leave space between the bus bar and the EC device (as the bus bar is only supposed to touch the lower conductive layer). When the bus bar width is fully accommodated by the BPE, that is, the bus bar is entirely atop the lower conductor, the outer edge, along the length, of the bus bar may be aligned with the outer edge of the BPE, or inset by about 1 mm to about 3 mm. Likewise, the space between the bus bar and the EC device is between about 1 mm and about 3 mm, in another embodiment between about 1 mm and 2 mm, and in another embodiment about 1.5 mm. Formation of BPEs is described in more detail below, with respect to an EC device having a lower electrode that is a TCO. This is for convenience only, the electrode could be any suitable electrode for an optical device, transparent or not.

To make a BPE, an area of the bottom TCO (e.g. first TCO) may be cleared of deposited material so that a bus bar can be fabricated on the TCO. This may be achieved by laser processing which selectively removes the deposited film layers while leaving the bottom TCO exposed in a defined area at a defined location.

The electromagnetic radiation used to fabricate a BPE may be the same as described above for performing LED. That is, laser ablation, performed from either the glass side or the film side, may be contemplated. Conventionally, the energy density required to ablate the film thickness has been achieved by passing the laser beam through an optical lens. The lens focuses the laser beam to the desired shape and size. For example, a “top hat” has been used having the dimensions described above, having an energy density of between about 0.5 J/cm2 and about 4 J/cm2. Moreover, laser scan overlapping for BPE has been proposed as described above for laser edge deletion. In certain embodiments, variable depth ablation may be used for BPE fabrication.

Referring again to FIGS. 4A and 4B, after forming the BPE, bus bars may applied to the device, one on exposed area 435 of the first conductor layer (e.g., first TCO) and one on the opposite side of the device, on the second conductor layer (e.g., second TCO), on a portion of the second conductor layer that is not above the first conductor layer, see 425.

FIG. 4B indicates cross-section cuts Z-Z′ and W-W′ of device 440. The cross-sectional views of device 440 at Z-Z′ and W-W′ are shown in FIG. 4C. The depicted layers and dimensions are not to scale, but are meant to represent functionally the configuration. In this example, the diffusion barrier was removed when width A and width B were fabricated. Specifically, perimeter area 140 is free of first conductor layer and diffusion barrier; although in some examples the diffusion barrier may be left intact to the edge of the substrate about the perimeter on one or more sides. In another example, the diffusion barrier may be co-extensive with the one or more material layers and the second conductor layer (thus width A is fabricated at a depth to the diffusion barrier, and width B is fabricated to a depth sufficient to remove the diffusion barrier). In this example, there is an overlapping portion, 445, of the one or more material layers about three sides of the functional device. On one of these overlapping portions, on the second TCO, bus bar 1 is fabricated.

FIG. 4C depicts the device layers overlying the first TCO, particularly the overlapping portion, 445. Although not to scale, cross section Z-Z′ for example, depicts the conformal nature of the layers of the EC stack and the second TCO following the shape and contour of the first TCO including the overlapping portion 445.

Conventionally, one or more laser isolation scribes have been required, depending upon design tolerances, material choice and the like. FIG. 4D depicts top-views of three devices, 440 a, 440 b and 440 c, each of which are variations on device 440 as depicted in FIGS. 4B and 4C. Device 440 a is similar to device 440, but includes L2 scribes (see above) that isolate first portions of the EC device along the sides orthogonal to the sides with the bus bars. Device 440 b is similar to device 440, but includes an L3 scribe isolating and deactivating a second portion of the device between the bus bar on the first (lower) conductor layer and the active region of the device. Device 440 c is similar to device 440, but includes both the L2 scribes and the L3 scribe. Although the scribe line variations in FIG. 4D are described in reference to devices 440 a, 440 b and 440 c, these variations can be used for any of the optical devices and lites of embodiments described herein.

Whatever the shape of the device, it can be incorporated into an insulated glass unit. Preferably, the device is configured inside the IGU so as to protect it from moisture and the ambient. FIG. 4E depicts IGU fabrication where the optical device, e.g. an electrochromic device is sealed within the IGU. IGU, 460, including a first substantially transparent substrate, 445, a spacer, 450, and a second substantially transparent substrate, 455. Substrate 445 has an electrochromic device fabricated thereon (bus bars are shown as dark vertical lines on substrate 445). When the three components are combined, where spacer 450 is sandwiched in between and registered with substrates 445 and 455, IGU 460 is formed. The IGU has an associated interior space defined by the faces of the substrates in contact with adhesive sealant between the substrates and the interior surfaces of the spacer, in order to hermetically seal the interior region and thus protect the interior from moisture and the ambient. This is commonly referred to as the primary seal of an IGU. A secondary seal includes an adhesive sealant applied around the spacer and between the panes of glass (the spacer has smaller length and width than the substrates so as to leave some space between the glass substrates from the outer edge to the spacer; this space is filled with sealant to form the secondary seal). In certain embodiments, any exposed areas of the first conducting layer are configured to be within the primary seal of the IGU. In one embodiment, any bus bars are also configured to be within the primary seal of the IGU. In one embodiment, the area of the second conductor layer that is not over the first conductor layer is also configured to be within the primary seal of the IGU. Conventional electrochromic IGU's configure the bus bars either outside the spacer (in the secondary seal) or inside the spacer (in the interior volume of the IGU) in the viewable area of the IGU (sometimes one in the secondary seal, the other in the viewable area). Conventional electrochromic IGU's also configure the EC device edges either running to the substrate edge or inside the spacer (within the interior volume of the IGU). The inventors have found it advantageous to configure the bus bars, laser scribes, and the like to be under the spacer, so as to keep them from the viewable area and, e.g., to free up the secondary seal so that electrical components therein do not interfere with the aforementioned features. Such IGU configurations are described in U.S. patent application Ser. No. 13/456,056, titled “Electrochromic Window Fabrication Methods,” filed Apr. 25, 2012, which is hereby incorporated by reference in its entirety. Controllers that fit into the secondary seal are described in U.S. Pat. No. 8,213,074, titled “Onboard Controllers for Multistate Windows,” filed Mar. 16, 2011, which is hereby incorporated by reference in its entirety. Methods described herein include sealing any exposed areas of the first conductor layer, edges of the device or overlapping regions of the one or more material layers, and the second conductor layer in the primary seal of the IGU. With or without a vapor barrier layer, such as silicon oxide, silicon aluminum oxide, silicon oxynitride, and the like, this sealing protocol provides superior moisture resistance to protect the electrochromic device while maximizing viewable area.

In certain embodiments, the fabrication methods described herein are performed using large-area float glass substrates, where a plurality of EC lites are fabricated on a single monolithic substrate and then the substrate is cut into individual EC lites. Similar, “coat then cut” methods are described in U.S. Pat. No. 8,164,818, filed Nov. 8, 2010, and titled, “Electrochromic Window Fabrication Methods,” which is hereby incorporated by reference in its entirety. In some embodiments, these fabrication principles are applied to the methods described herein, e.g., in relation to FIGS. 4A-4D.

FIGS. 4F and 4G depict an EC lite fabrication process flow, similar to that described in relation to FIG. 4A, but carried out on a large-area substrate as applied to coat then cut methods, according to some examples. These fabrication methods can be used to make EC lites of varying shapes, e.g., as described herein, but in this example, rectangular EC lites are described. In this example, substrate 430 (e.g. as described in relation to FIG. 4A, coated with a transparent conducting oxide layer) is a large-area substrate, such as float glass, e.g. a sheet of glass that is 5 feet by 10 feet. Analogous to operation 405 as described in relation to FIG. 4A, edge deletion at a first width, A, is performed. Edge taper and/or polish may also be performed. In this example, since there are to be a plurality of EC devices (in this example, 12 devices) fabricated on a large substrate, the first width A may have one or more components. In this example, there are two components, A1 and A2, to width A. First, there is a width A1, along the vertical (as depicted) edges of the substrate. Since there are neighboring EC devices, the width A1 is reflected in a coating removal that is twice the width A1. In other words, when the individual devices are cut from the bulk sheet, the cuts in between neighboring devices along the vertical (as depicted) dimension will evenly bi-furcate the area where the coating is removed. Thus “edge deletion” in these areas accounts for where glass edges will eventually exist after the glass is cut (see for example FIG. 4G). Second, along the horizontal dimension, a second A-width component, A2, is used. Note, although width A1 may be applied about the entire perimeter of the substrate, in the illustrated example more width is provided to accommodate the bus bar that will fabricated on the top transparent conductor layer (e.g. see FIG. 4C, bus bar 1). In this example, width A2 is the same both at the top and bottom edge of the substrate and between neighboring EC devices. This is because the fabrication is analogous to that described in relation to FIG. 4B, i.e., where the EC devices are cut from the substrate along the bottom of edge of the transparent conductor area for each device (see FIG. 4D).

Next, in operation 410, the remaining layers of the EC device are deposited over the entire substrate surface (save any areas where clamps might hold the glass in a carrier, for example). The substrate may be cleaned prior to operation 410, e.g., to remove contaminants from the edge deletion. Also edge taper on each of the TCO areas may be performed. The remaining layers of the EC device encapsulate the isolated regions of the transparent conductor on the substrate, because they surround these areas of transparent conductor (except for the back face which resides against the substrate or intervening ion barrier layer). In one example, operation 410 is performed in a controlled-ambient all PVD process, where the substrate doesn't leave the coating apparatus or break vacuum until all the layers are deposited.

In operation 415, edge deletion at a second width, B, narrower than the first width A, is performed. In this example, second width B is uniform. In between neighboring devices, second width B is doubled to account for cutting the substrate along lines evenly between two devices so that the final devices have a uniform edge delete about them for the spacer to seal to the glass when an IGU is fabricated from each EC device. As illustrated in FIG. 4F, this second edge deletion isolates individual EC lites on the substrate. In some examples, the second width B may be much smaller than that needed to accommodate a spacer for IGU fabrication. That is, the EC lite may be laminated to another substrate and thus only a small edge delete at width B, or in some embodiments no edge delete at the second width B is necessary.

Referring to FIG. 4G, operation 420 includes fabricating a BPE, 435, where a portion of the EC device layers are removed to expose the lower conductor layer proximate the substrate. In this example, that portion is removed along the bottom (as depicted) edge of each EC device. Next, during operation 425, bus bars are added to each device. In certain embodiments, the EC lites are excised from the substrate prior to bus bar application. The substrate now has completed EC devices. Next, the substrate is cut, operation 470, to produce a plurality of EC lites 440, in this example 12 lites. In certain embodiments the individual EC lites are tested and optionally any defects mitigated prior to cutting the large format sheet.

Coat and then cut methods allow for high throughput manufacture because a plurality of EC devices can be fabricated on a single large area substrate, as well as tested and defect-mitigated prior to cutting the large format glass sheet into individual lites. For example, the large format glass pane may be laminated with individual strengthening panes registered with each EC device prior to cutting the large format sheet. The bus bars may or may not be attached prior to lamination; for example, the mate lite may be coextensive with an area allowing some exposed portions of the top and bottom TCO's for subsequent bus bar attachment. In another example, the mate lite is a thin flexible material, such as a thin flexible glass described below, which is substantially co-extensive with the EC device or the entire large format sheet. The thin flexible mate lite is ablated (and lamination adhesive, if present in these areas) down to the first and second conductor layers so that bus bars may be attached to them as described herein. In yet another embodiment, the thin flexible mate lite, whether co-extensive with the entire large format sheet or the individual EC devices, is configured with apertures which are registered with the top conductor layer and the BPE during lamination. The bus bars are attached either before or after lamination with the mate lite, as the apertures allow for either operation sequence. The lamination and bus bar attachment may separately be performed prior to cutting the large sheet, or after.

As indicated above, in the absence of the presently disclosed techniques, laser ablation techniques for multi-layer thin-film devices having one or more material layers sandwiched between two thin-film electrical conductor layers contemplated a focused laser beam. The focused laser beam contemplated a focus area (spot size) of, for example, about 0.005 mm2 to about 2 mm2. This focusing level was selected to achieve the required energy density to ablate the EC film stack. For example the energy density used in the ablation may be in the range of about 20 mJ/mm2 to about 60 mJ/mm2 (i.e., the corresponding laser energy is about 0.1 to 120 mJ). Relatively short pulse durations of 10-11 seconds to 5*10-8 seconds were contemplated to be applied at a relatively high frequency (>KHz).

The present inventors have appreciated that, advantageously, a higher energy laser (about 300-1500 mJ vs 10-50 mJ) may be applied in a collimated (defocused) manner to provide a larger spot size (e.g., at least about 0.2 cm2 vs <1 mm2). Longer duration pulses (e.g., tens of nano seconds) applied at a lower frequency (e.g., about 1-1000 Hz, in some implementations) have also been found to be advantageous. Advantageously, the contemplated laser operating parameters provide for an average energy density similar to those described above in connection with prior art.

The present inventors have found that such a high energy, non-focused laser may be configured to ablate material from a several millimeters spot diameter in as little as a single pulse. Moreover, the present techniques reduce complexity of the apparatus by obviating a need for focusing lenses, autofocus apparatus and the like. Furthermore, the larger spot size reduces or even eliminates any need for raster scanning while providing a BPE width that fully accommodates the bus bar and allows conservative separation between the bus bar and BPE edge. For example, in some embodiments the separation may be about 4 mm, which is wide enough to avoid the electrical contact with upper conductor.

In some implementations, a dual wavelength laser may be contemplated, so as to improve energy absorption of different layers of the multi-layer stack. For example, a laser simultaneously outputting light of 1064 nm wavelength and 532 nm wavelength has been considered.

FIG. 5 illustrates a comparison of laser ablation according to the prior art with the presently disclosed techniques for a workpiece including glass substrate 505 on which is disposed diffusion barrier layer 501 between the glass substrate 505 and a first TCO layer 515 and an EC stack 525 disposed between the first TCO layer 515 and a second TCO layer 530. In Detail A, according to the prior art, three discrete laser ablation areas are required (L3, BPE and LED). Detail B illustrates that the present techniques facilitate the omission of the L3 ablation area (isolation scribe). This is because, advantageously, edges of the ablation area formed by the unfocused laser beam (which has a Gaussian energy distribution) are sloped (as opposed to having vertical edges). As a result, a greater separation between exposed conductive layers is assured, and a need for an additional electrical isolation scribe is eliminated.

The BPE area may have a width of about 6 mm in some implementations. In the absence of the presently disclosed techniques such a width may be approximately 10 times the diameter of the focused laser beam's spot diameter. As a result raster scanning of the laser beam and/or of the workpiece would conventionally be required in order to achieve the required width. Advantageously, the present techniques provide a collimated laser beam diameter approximately the same as the desired BPE area width and raster scanning may be avoided. As a result, apparatus complexity and fabrication processing time are both reduced.

Referring now to FIG. 6, a method 600 for fabricating an optical device will be described. As indicated above, the optical device may include a substrate and, sandwiched between a first conductive layer proximate to the substrate and a second conducting layer distal from the substrate, an electrochromic stack. At block 610, a first width of material may be removed from the second conductive layer and the electrochromic stack proximal to the perimeter of the substrate. A depth of removal may be sufficient to expose a portion of the first conductive layer

At block 620, second width of material, narrower than the first width, at the periphery of the substrate along substantially the entire perimeter of the substrate may be removed to a second depth, the second depth being at least sufficient to remove the first conducting layer.

At block 630 a bus bar may be applied to the exposed portion of the first transparent conducting layer. Advantageously, removing the first width and removing the second width is performed with a substantially collimated laser beam and configured as pulses of electromagnetic radiation having an energy density from about 1 J/cm2 to about 10 J/cm2 in a spot having a characteristic dimension of at least about 5 mm at the surface of the first conductive layer.

As used herein, the “characteristic dimension” of the laser spot may be the greatest distance between any two points on the spot. In the case of a generally circular or elliptical spot, the characteristic dimension may be a diameter. In the cases of a polygonal spot, the characteristic dimension may be the distance between two vertices. The boundary of the spot may be the location where intensity of the laser beam radiation drops to about 20% of its maximum. In certain embodiments, the spot produced by the pulses of electromagnetic radiation has a substantially square or rectangular shape.

Referring again to Detail B of FIG. 5, for a workpiece including glass substrate 505 on which is disposed diffusion barrier layer 510 between the glass substrate 505 and a first TCO layer 515 and an EC stack 525 disposed between the first TCO layer 515 and a second TCO layer 530 material may be removed by laser ablation to form laser ablation region BPE. Some laser ablation techniques contemplated by the present disclosure, particularly useful for forming the BPE area, may be conducted in a way that preserves, substantially untouched, the lower transparent conductive layer (first TCO 515), but selectively removes the layers above it. For example, the electrochromic (EC) stack layer 525, which includes at least an electrochromic layer and a counter electrode layer, and, if present, an upper transparent conductive layer (second TCO layer 530) may be removed by laser ablation while producing a smooth, undamaged, exposed upper surface of the first TCO layer 515. In other words, the disclosed laser ablation process provides for selective ablation in which material above the first TCO layer 515 (e.g., the second TCO layer 520 and the EC stack 510) may be reliably removed without damaging the first TCO layer 515.

In some embodiments, laser operating parameters are chosen to selectively ablate the second TCO layer 530 and the EC stack layer 525, while preserving the first TCO layer 515. As a result, the overall laser ablation process is simplified and may be performed more rapidly. In the absence of the present teachings, laser ablation processes are relatively non-selective (i.e., the laser will readily ablate any layer of the multi-layer stack) and/or selective methods operate on small areas, sequentially, and thus take more time. This presents challenges as the thickness and/or composition of the EC stack layer 525 and first TCO layer 515 may vary over the surface area of the multi-layer stack and from workpiece to workpiece. As a result, the depth of ablation, and surface roughness of an exposed surface may vary undesirably, or, to reach selective ablation it takes an inordinate amount of time, thus not suitable for high-throughput processing, e.g., in a manufacturing setting. For example, if a non-selective laser ablation process is not carefully controlled to account for variations in thickness and/or composition across an area to be ablated, some portions of the ablation area may not reach the depth of the top surface of the first TCO layer 515 and/or some portions of the ablation area may be undesirably thin or otherwise damage the first TCO layer 515. To avoid those defects, using existing methods requires long processing times to ablate any substantial area or multiple samples. This may be particularly problematic when processing a large-area glass substrate, such as float glass, e.g. a sheet of glass that is 5 feet by 10 feet, or when a high throughput rate is required.

The present inventors have found that a laser ablation process operating in the near-infrared wavelength range is effective to remove layers above, and extending down to the first TCO layer 515, while leaving the exposed top surface of the first TCO layer 515 smooth and undamaged. Generally, the contemplated laser ablation process operates in a selected near-infrared wavelength greater than about 0.8 μm wavelength. In certain embodiments, the selected wavelength range is about 0.8 μm to about 2.5 μm. Advantageously, the selected wavelength may be in the range of about 1.8 μm to about 2.2 μm. In one embodiment, a laser ablation process employs a thulium laser operating at a selected wavelength of about 1.95 μm. In another embodiment, a laser ablation process employs a holmium laser operating at a selected wavelength of about 2.05 μm.

Without being bound to the following theory, it is believed that the obtained selective ablation results from preferential reflection of laser light of the selected wavelength by the first TCO layer 515 combined with preferential absorption of the laser light of the selected wavelength by the EC stack 525. The theory may be better understood by referring to FIG. 7. Referring first to Detail C, a laser beam 7000C produced in the selected near-infrared wavelength is applied to the exposed (upper) surface of the second TCO layer 530. The laser beam removes material, first, from the second TCO layer 530, and, subsequently, from the EC stack 525. As the depth of ablation resulting from the laser beam approaches the interface between EC stack 525 and first TCO layer 515 (Detail D), it is believed that a significant fraction of the laser energy is reflected back toward the upper layers. Some of the reflected energy 7000D is reabsorbed by the ED stack 525 material above the first TCO layer 515. The reabsorption may result in rapid heating of that material and may create a shockwave directed away from the TCO layer 515. The shock wave and reflected laser beam 7000E1 (Detail E) contribute to particle ejection from at least the EC stack 525 while leaving the first TCO layer 515 relatively unaffected. It is believed that the first TCO layer 515 and layers below the first TCO layer 515 receive only a small part of the laser beam energy (the unreflected portion 7000E2) and this energy is insufficient to damage those layers. As a result, referring to Detail F, the first TCO layer 515 is exposed cleanly, with inconsequential residue or damage. It should be noted that, although FIG. 7 and the foregoing description assume a laser beam ablating the EC film stack by way of directing the laser beam through the EC film stack toward the glass 505, in some embodiments, a laser beam ablating the EC film stack may be directed through the glass 505 toward the EC film stack.

Because the laser beam is operated at a wavelength that selectively ablates only materials above the first TCO layer 515, the laser beam may operate at a relatively higher power density than would be possible in the absence of the presently disclosed techniques. Operation at relatively high power density is advantageous, at least because it results in increased processing speed. In the absence of the present teachings, a laser etch process operated at the power densities contemplated herein would pose an unacceptable risk of damaging the first TCO layer 515. For example, when operating at wavelength in the 0.5-0.6 μm range, the first TCO layer 515 may experience damage at energy densities as low as about 10 mJ/mm². The inventors have found, however, that at higher wavelengths, for example around 2 μm, the first TCO layer suffers negligible ablation at energy densities as high as, for example, 150 mJ/mm². Thus, a more robust laser ablation process may be obtained that produces a better quality finished workpiece.

In some implementations, the higher power density results from more narrowly focusing a conventional laser beam. For example, a conventional laser beam having a diameter in approximately the range of about 0.5-0.6 mm may be focused down to a spot diameter at the workpiece surface of about 0.05-0.15 mm.

In some implementations, a focused laser beam may have a focus area (spot size) of, for example, about 0.005 mm² to about 80 mm². This focusing level was selected to achieve the required energy density to ablate the EC film stack. For example, the energy density used in the ablation may be in the range of about 70 mJ/mm2 to about 200 mJ/mm2 (i.e., the corresponding laser energy is about 0.1 to 80 mJ). Relatively short pulse durations of 5 to 100 nanoseconds were contemplated to be applied at a relatively high frequency (>KHz).

Benefits of the present techniques may be better appreciated by referring to FIG. 8, which illustrates a comparison between a depth profile of an ablation region (scribe line) produced by conventional ablation techniques (Detail G) and that of a scribe line produced by the presently disclosed techniques (Detail H). It may be observed that the depth profile shown in Detail G has distinct variations that are almost entirely absent in the depth profile shown in Detail H.

FIG. 9A illustrates a cross-section view of a scribe line formed using the present ablation techniques to selectively remove material above but not including the first TCO layer 515. It may be observed that depth variations across a 10 mm wide scribe line are less than about 0.01 μm. This is consistent with a desired outcome of removing virtually all material above the TCO layer 515, while avoiding removal of any but a negligible portion of TCO layer 515. For comparison purposes, FIG. 9B illustrates a cross-section view of a scribe line formed using conventional techniques. It may be observed that, in the absence of the present teachings, depth variations on the order of 0.5 μm may be experienced.

Whereas the preceding examples illustrated ablation regions with “vertical” sidewalls (approximately orthogonal to the substrate), tapered or stepped sidewalls are likewise within the contemplation of the present disclosure. As indicated hereinabove such tapered or stepped sidewalls may, advantageously, provide a greater separation between exposed conductive layers and thereby avert a need for an additional electrical isolation scribe is eliminated. FIG. 10 illustrates two examples of how tapered or stepped sidewalls may be obtained. Referring first to Detail J, a stepped profile may be obtained by scanning two or more line-like ablation regions, at different powers. In the illustrated example, a lower power beam 1001 produces a first ablation region 1011, and a higher power beam 1002 produces a second ablation region 1012 that is deeper than the first ablation region 1011. Alternatively, or in addition, referring now to Detail K, a laser beam power profile may be structured so as to provide different powers at different locations in the same beam. As a result, a stepped profile similar to Detail J may be obtained without necessarily requiring a scanner.

Although FIG. 10 depicts a stepped profile, it will be appreciated that a smooth taper such as shown in Detail B of FIG. 5 may be approximated by making the steps sufficiently small, or by configuring the beam to have a Gaussian energy distribution as described hereinabove.

Referring now to FIG. 11, a method 1100 for fabricating an optical device will be described. As indicated above, the optical device may include a glass substrate and, sandwiched between a first conductive layer proximate to the substrate and a second conducting layer distal from the substrate, an electrochromic stack. At block 1110, a laser beam may be directed from a laser source onto a surface of a workpiece to remove material from the workpiece. As disclosed hereinabove, the laser beam, advantageously, has a selected near-infrared wavelength greater than about 1.4 μm. The workpiece may include an electrochromic device or a partially fabricated electrochromic device on a transparent substrate, and the material removed may include one or more layers of the electrochromic device. The electrochromic device may include an electrochromic stack disposed between a first transparent conductive layer, distal from the laser source, and a second transparent conductive layer, proximal to the laser source.

At block 1120, a portion of the second transparent conductive layer and a portion of the electrochromic stack is removed without damaging the first transparent conductive layer.

CONCLUSION

It should be understood that the certain embodiments described herein can be implemented in the form of control logic using computer software in a modular or integrated manner. Based on the disclosure and teachings provided herein, a person of ordinary skill in the art will know and appreciate other ways and/or methods to implement the present invention using hardware and a combination of hardware and software.

Any of the software components or functions described in this application, may be implemented as software code to be executed by a processor using any suitable computer language such as, for example, Java, C++ or Python using, for example, conventional or object-oriented techniques. The software code may be stored as a series of instructions, or commands on a computer-readable medium, such as a random-access memory (RAM), a read-only memory (ROM), a magnetic medium such as a hard-drive or a floppy disk, or an optical medium such as a CD-ROM. Any such computer readable medium may reside on or within a single computational apparatus, and may be present on or within different computational apparatuses within a system or network.

Although the foregoing embodiments have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, and apparatus of the present embodiments. Additionally, one or more features from any embodiment may be combined with one or more features of any other embodiment without departing from the scope of the disclosure. Further, modifications, additions, or omissions may be made to any embodiment without departing from the scope of the disclosure. The components of any embodiment may be integrated or separated according to particular needs without departing from the scope of the disclosure. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the embodiments are not to be limited to the details given herein. 

What is claimed is:
 1. A method of removing material from a workpiece, the method comprising: directing a laser beam from a laser source onto a surface of the workpiece, wherein the laser beam comprises projected light, the projected light having a selected near-infrared wavelength in the range of about 1.4 to about 3 μm.
 2. The method of claim 1, wherein the workpiece comprises an electrochromic device or a partially fabricated electrochromic device on a transparent substrate, and the material comprises one or more layers of the electrochromic device.
 3. The method of claim 2, wherein removing the material produces an ablation region on the one or more layers of the electrochromic device, the ablation region having at least one edge.
 4. The method of claim 3, wherein the edge is approximately orthogonal to the one or more layers.
 5. The method of claim 3, wherein the edge has a stepped or tapered profile.
 6. The method of claim 1, wherein removing the material forms a bus bar pad expose region.
 7. The method of claim 6, wherein: the workpiece comprises an electrochromic device including an electrochromic stack disposed between a first transparent conductive layer, distal from the laser source, and a second transparent conductive layer, proximal to the laser source; and removing the material comprises removing a portion of the second transparent conductive layer and a portion of the electrochromic stack to expose a surface of the first transparent conductive layer without damaging the first transparent conductive layer.
 8. The method of claim 7, wherein the bus bar pad expose region comprises an exposed portion of the surface of the first transparent conductive layer.
 9. The method of claim 1, wherein the selected near-infrared wavelength is within a range of 1.8 μm to 2.2 μm.
 10. The method of claim 1, wherein the laser beam removes the material from the workpiece by ablation.
 11. The method of claim 1, wherein removing the material does not comprise moving the laser beam in a raster scan.
 12. The method of claim 1, wherein the laser source comprises a thulium laser operating at a selected wavelength of about 1.95 μm or a holmium laser operating at a selected wavelength of about 2.05 μm.
 13. The method of claim 1, wherein the laser source is configured to deliver a pulsed laser beam, each pulse having an energy in a range of about 0.2 to 1500 mJ.
 14. The method of claim 13, wherein each pulse has a duration of from about 1 ns to about 100 ns.
 15. The method of claim 13, wherein the pulsed laser beam has a pulse repetition rate of about 1 to 100,000 Hz.
 16. The method of claim 1, wherein the workpiece includes a large-area float glass substrate.
 17. The method of claim 16, wherein the float glass substrate has a surface area greater than 40 square feet.
 18. A material removal system comprising: a laser source configured to direct a laser beam onto a surface of a workpiece, wherein the laser beam comprises projected light, the projected light having a selected near-infrared wavelength the range of about 1.4 to about 3 μm; and a workpiece holder; wherein: the laser source and the workpiece holder are configured such that, during operation, the laser beam ablates material from the workpiece.
 19. The system of claim 18, wherein the workpiece comprises an electrochromic device or a partially fabricated electrochromic device on a transparent substrate, and the material comprises one or more layers of the electrochromic device.
 20. The system of claim 19, wherein removing the material produces an ablation region on the one or more layers of the electrochromic device, the ablation region having at least one edge.
 21. The system of claim 20, wherein the edge is approximately orthogonal to the one or more layers.
 22. The system of claim 20, wherein the edge has a stepped or tapered profile.
 23. The system of claim 18, wherein removing the material forms a bus bar pad expose region.
 24. The system of claim 23, wherein: the workpiece comprises an electrochromic device including an electrochromic stack disposed between a first transparent conductive layer, distal from the laser source, and a second transparent conductive layer, proximal to the laser source; and removing the material comprises removing a portion of the second transparent conductive layer and a portion of the electrochromic stack to expose a surface of the first transparent conductive layer without damaging the first transparent conductive layer.
 25. The system of claim 24, wherein the bus bar pad expose region comprises an exposed portion of the surface of the first transparent conductive layer.
 26. The system of claim 18, wherein the laser source comprises a thulium laser operating at a selected wavelength of about 1.95 μm or a holmium laser operating at a selected wavelength of about 2.05 μm.
 27. The system of claim 18, wherein the laser source is configured to deliver a pulsed laser beam, each pulse having an energy in a range of about 0.2 to 1500 mJ.
 28. The system of claim 27, wherein each pulse has a duration of from about 1 ns to about 100 ns.
 29. The system of claim 27, wherein the pulsed laser beam has a pulse repetition rate of about 1 to 100,000 Hz.
 30. The system of claim 18, wherein the workpiece includes a large-area float glass substrate.
 31. A structure comprising: a substrate; and an electrochromic device disposed on the substrate, the electrochromic device including one or more layers configured as an electrochromic stack disposed between a first transparent conductive layer, distal from a laser source, a second transparent conductive layer, proximal to the laser source, and an ablation region; wherein: the ablation region is produced by removing a portion of the second transparent conductive layer and a portion of the electrochromic stack without damaging the first transparent conductive layer.
 32. The structure of claim 31, wherein the ablation region has at least one edge.
 33. The structure of claim 32, wherein the edge is approximately orthogonal to the one or more layers.
 34. The structure of claim 32, wherein the edge has a stepped or tapered profile.
 35. The structure of claim 31, wherein the ablation region comprises a bus bar pad expose region.
 36. The structure of claim 35, wherein the bus bar pad expose region comprises an exposed portion of the first transparent conductive layer.
 37. The structure of claim 31, further comprising a large-area float glass substrate.
 38. The structure of claim 37, wherein the float glass substrate has a surface area greater than 40 square feet.
 39. A method of fabricating an optical device, the method comprising: removing material from the optical device by directing a laser beam from a laser source onto a surface of the optical device, the optical device comprising a substrate and an electrochromic stack, the electrochromic stack being disposed between a first transparent conductive layer, distal from the laser source, and a second transparent conductive layer, proximal to the laser source; wherein removing the material comprises removing a portion of the second transparent conductive layer and a portion of the electrochromic stack without damaging the first transparent conductive layer; and the laser beam comprises projected light, the projected light having a selected near-infrared wavelength in the range of about 1.4 to about 3 μm.
 40. The method of claim 39, wherein removing the material produces an ablation region on the electrochromic stack, the ablation region having at least one edge.
 41. The method of claim 40, wherein the material comprises one or more layers of the optical device and the at least one edge is approximately orthogonal to the one or more layers.
 42. The method of claim 40, wherein the edge has a stepped or tapered profile.
 43. The method of claim 39, wherein removing the material forms a bus bar pad expose region.
 44. The method of claim 43, wherein the bus bar pad expose region comprises an exposed portion of the surface of the first transparent conductive layer.
 45. The method of claim 39, wherein the laser source comprises a thulium laser operating at a selected wavelength of about 1.95 μm or a holmium laser operating at a selected wavelength of about 2.05 μm.
 46. The method of claim 39, wherein the laser source is configured to deliver a pulsed laser beam, each pulse having an energy in a range of about 0.2 to 1500 mJ.
 47. The method of claim 46, wherein each pulse has a duration of from about 1 ns to about 100 ns.
 48. The method of claim 46, wherein the pulsed laser beam has a pulse repetition rate of about 1 to 100,000 Hz. 